Techniques Of Farming And Cultivation In Reducing Contents Of Cadmium And Lead Of Rice And Their Mechanism

In order to find out the pollution status of cadmium and lead in rice production in Qujiang district,Shaoguan city,Guangdong province,samples of soil,fertilizer,water,and brown rice were collected from rice growing area and analyzed.Additionally,techniques and mechanism of farming and cultivation in reducing contents of cadmium(Cd)and lead(Pb)of rice were explored.In this study,the field and pot experiments were performed in order to screen out rice varieties with low-cadmium and/or low-lead accumulation.Effects of ratoon rice and different farming modes on cadmium and lead accumulation in rice were examined.Effects of ultrasonic seed treatment on the accumulation of cadmium and lead in rice were analyzed.The major results are shown as follows:(1)Before applying techniques of farming and cultivation in reducing contents of cadmium and lead of rice,in rice growing area in Qujiang district,Shaoguan city,Guangdong province,the soil p H ranged from 4.50 to 5.62 with an average of 4.93,indicating that the soil was acidic.The concentration ranges of Cd and Pb in topsoil were 0.115 ~ 6.128 and 17.545 ~ 110.294 mg/kg,respectively.The concentration ranges of Cd and Pb in 100 water samples were 0.0096 ~ 0.0593 and 0.0120 ~ 0.2308 mg/L,respectively.The contents in 150 brown rice samples ranged from 0.015 to 3.668 mg/kg for Cd and from 0.091 to 2.329 mg/kg for Pb,and the variation range of those measured values became larger.The content ranges of Cd and Pb in 52 samples included 7 types fertilizers were 0.054 ~ 1.142 and 1.138 ~ 16.739 mg/kg,respectively.The organic-inorganic compound fertilizer was the highest Cd content,followed by the soil conditioner,the superphosphate,and potassium chloride.The highest Pb content was the soil conditioner and followed by the organic fertilizer,superphosphate,and potassium chloride,three-nutrient compound fertilizer.However,the contents of Cd and Pb in fertilizers were lower than the permissible limit as describe by Ecological Index of Arsenic,Cadmium,Lead,Chromium and Mercury for Fertilizers(GB/T 23349-2009).(2)Field and pot experiments of cultivar selection were conducted.The results showed that four rice cultivars,i.e.Guangyan1,Guixiangzhan,Huahang31,and Huahangsimiao were low-Cd and low-Pb accumulation cultivars and fine grain quality.(3)The pot experiment showed that the trend for the average values of Cd contents in different plant parts was recorded as root > stem > sheath > leaf > spike > rice bran > brown rice > rice hull.Meanwhile,the average values of Pb content in different parts of rice were as follows: root > sheath > leaf > stem > rice bran > rice bran > brown rice > rice hull.For the full heading stage,15 days after full heading and maturity,Cadmium and lead stress increased the activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX)in rice flag leaves,increased the contents of malondialdehyde(MDA),soluble protein,proline,glutathione(GSH),and metallothionein(MT),reduced the photosynthetic efficiency,weakened the root bleeding intensity and root vigor,and reduced the total root length,total root surface area,and total root volume,resulting in a decrease in yield.(4)The pot experiment of regenerated rice showed that the contents of Cd and Pb in the brown rice of Huahang31,Chaoyou1000 and Hemeizhan in the ratoon season were significantly lower than those in the first season.Meanwhile,the yield and yield components in the ratoon season were significantly lower than that in the first season.(5)The field experiment of both treatments,i.e.winter fallow-rice(WF)and rape-rice rotation(CR)was carried out.The results showed that the CR treatment significantly reduced the contents of Cd and Pb in roots,stems and sheath,leaf,spike and brown rice of Guangyan1 and Huahang31,resulting in a decline in the total accumulation of Cd and Pb.The CR treatment increased the rice yield,effective spike number,total grain number per panicle and seed setting rate,but reduced the 1000-grain weight.The CR treatment improved rice quality,increased brown rice rate,head rice rate and protein content,and significantly reduced chalky rice rate and chalkiness of rice.Removing rape straw in winter coud reduce the content of cadmium and lead in soil.(6)The germination test showed that ultrasonic treatment can promote seed germination,increase seed germination rate,promote root elongation and shoot growth,increase fresh weight and dry matter weight in root and shoot under Cd and/or Pb stress.(7)The contents of proline,GSH,MT,and soluble protein,as well as the activities of SOD,CAT,and APX were substantially higher whilst the MDA contents were prominently lower in ultrasonic treatment than that in the control.Moreover,the ultrasonic treatment increased the effective spike number,total grain number per panicle,seed setting rate,and the 1000-grain weight,resulting in an increase rice yield.The ultrasonic treatment improved rice quality,increased brown rice rate and head rice rate,whereas significantly reduced chalky rice rate and chalkiness of rice.